8:46 a.m.-8:47 a.m. September 11, 2001: Flight 175 Changes Transponder Signal but Remains Easily Traceable

Flight 175 stops transmitting its transponder signal. It is currently flying near the New Jersey-Pennsylvania border. [Guardian, 10/17/2001; Newsday, 9/10/2002; 9/11 Commission, 6/17/2004 ] However, the transponder is turned off for only about 30 seconds, and then comes back on as a signal that is not designated for any plane on this day. Then, within the space of a minute, it is changed to another new code. But New York Center air traffic computers do not correlate either of these new transponder codes with Flight 175. Consequently, according to an early FAA report, “the secondary radar return (transponder) indicating aircraft speed, altitude, and flight information began to coast and was no longer associated with the primary radar return.” Therefore, while controllers are able “to track the intruder easily… they couldn’t identify it.” However, Dave Bottiglia, the New York Center air traffic controller responsible for Flight 175, is currently trying to locate the already-crashed Flight 11, and therefore supposedly does not notice the transponder code changes on Flight 175 until 8:51 a.m. (see 8:51 a.m.-8:53 a.m. September 11, 2001). [Federal Aviation Administration, 9/17/2001 ; Washington Post, 9/17/2001; 9/11 Commission, 8/26/2004, pp. 21] According to a “Flight Path Study” by the National Transportation Safety Board, the change of Flight 175’s transponder code is the “first indication of deviation from normal routine.” [National Transportation Safety Board, 2/19/2002 ]